An impeachment case against Sereno alleged that she misdeclared some P30 million in earnings for serving as government counsel in an arbitration case and that she did not pay the corresponding taxes.

BIR Deputy Commissioner Arnel Guballa said his agency already started collating documents on the Chief Justice's income, but has yet to launch a formal inquiry.

House justice panel chair Reynaldo Umali then ordered the BIR to submit a summary report of Sereno's income and tax payments by February 19.

Guballa said his agency "will try our best" to meet the deadline.

"When I come back to office then we will initiate the issuance of the letter of authority and we will serve this to the Chief Justice, the letter of investigation," he said.

"That will formalize the audit then with the powers of the BIR, we can get all the incomes that the Chief Justice has made."

Guballa at the start of the hearing submitted to the panel Sereno's income tax returns (ITRs) from 2004 to 2010, which covers the payment she received for the case against the Philippine International Air Terminals Co. Inc. (Piatco) over the controversial Ninoy Aquino International Airport Terminal 3.

"Chief Justice Sereno has accurately and properly declared all her earnings as government co-legal counsel in the PIATCO cases," lawyer Josa Deinla, a spokesperson for Sereno, said in a statement Wednesday.

Deinla added that the BIR has not served any deficiency assessment notice to Sereno during the years she filed her income tax returns.

"This only means one thing: All her income tax filings when she was a private lawyer were accurate and proper," she said.

"We are confident that the plan of the House committee to have the CJ’s ITR filings looked into by the BIR would prove that the Chief Justice had paid the corresponding taxes for the income she earned while in private law practice," she added.